Feeding comminuted fibrous material

ABSTRACT

A system and method for feeding comminuted cellulosic fibrous material such as wood chips to the top of a treatment vessel such as a continuous digester provide enhanced simplicity, operability, and maintainability by eliminating the high pressure transfer device conventionally used in the prior art. Instead of a high pressure transfer device the steamed and slurried chips are pressurized using one or more slurry pumps located at least thirty feet below the top of the treatment vessel and for pressurizing the slurry to a pressure of at least about 10 bar gauge. A return line from the top of the digester may, but need not necessarily, be operatively connected to the one or more pumps and if connected to the pumps, the liquid in the return line may be cooled to a temperature at which it will not flash during handling. Recirculation loops may be established associated with one or all of the slurry pumps to facilitate startup. A static flow splitter may be provided to split the flow from the last pump to two or more digesters.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 09/063,429 filed Apr. 21, 1998, now Patent No. ______, which in turnis a continuation-in-part of Ser. No. 08/738,239 filed Oct. 25, 1996,now U.S. Pat. No. 5,753,075.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] This invention relates to a method and system for feedingcomminuted cellulosic fibrous material to a treatment vessel, such as acontinuous digester. The invention simplifies and dramatically reducesthe number of components needed when compared to the existing art.

[0003] U.S. Pat. Nos. 5,476,572, 5,622,598 and 5,635,025 and 5,766,418introduced the first real breakthroughs in the art of feeding comminutedcellulosic fibrous material to a treatment vessel in over forty years.These patents and the application disclose several embodiments,collectively marketed under the trademark Lo-Level® feed system byAhlstrom Machinery Inc. of Glens Falls, N.Y., for feeding a digesterusing a slurry pump, among other components. As described in thesepatents and application, using such a pump to feed a slurry to ahigh-pressure transfer device dramatically reduces the complexity andphysical size of the system needed, and increases the ease ofoperability and maintainability. The prior art systems employing ahigh-pressure transfer device, for example a High-Pressure Feeder assold by Ahlstrom Machinery Inc., but without such a pump, areessentially unchanged from the systems sold and built since the 1940sand 1950s.

[0004] The present invention relates to an even more dramaticimprovement to the methods and systems disclosed in the above-mentionedpatent and applications. The present invention actually eliminates theneed for transfer devices, such as a High-Pressure Feeder, by usinghigh-pressure pumping devices to transfer a slurry of comminutedcellulosic fibrous material directly to a digester.

[0005] The reaction of pulping chemicals with comminuted cellulosicfibrous material to produce a chemical pulp requires temperaturesranging between 140-180° C. Since the aqueous chemicals used to treatthe material would boil at such temperatures, commercial chemicalpulping is typically performed in a pressure-resistant vessel underpressures of at least about 10 bars gauge (approximately 150 psi gauge).In order to maintain this pressure, especially when performing acontinuous pulping process, special accommodations must be made toensure that the pressure is not lost when introducing material to thepressure vessel. In the prior art this was accommodated by what is knownin the art as a “High-Pressure Feeder”. This feeder is aspecially-designed device containing a pocketed rotor which acts as ameans for transferring a slurry of material from a low pressure to ahigh pressure while also acting as a valve for preventing loss ofpressure. This complicated and expensive device has long been recognizedas an essential component for introducing slurries of comminutedcellulosic material to pressurized vessels, typically at elevatedtemperatures, especially to continuous digesters.

[0006] According to the invention a system which replaces theHigh-Pressure Feeder—which has been recognized for over forty years asbeing essential to continuous digesting—is provided, greatly simplifyingconstruction of a pulp mill.

[0007] According to one aspect, a system for producing chemicalcellulose pulp from comminuted fibrous cellulose material, such as woodchips, comprises the following components: A steaming vessel in whichcomminuted fibrous cellulose material is steamed to remove the airtherefrom. A superatmospheric pressure vertical treatment vessel havingan inlet for a slurry of comminuted cellulose fibrous material at a topportion thereof and an outlet at a bottom portion thereof. And,pressurizing transfer means for pressurizing a slurry of material fromthe steaming vessel and transferring it to the treatment vessel inlet,the pressurizing transfer means consisting of one or more high pressureslurry pumps located below the top portion of the treatment vessel.

[0008] The one or more pumps preferably comprises first and second highpressure slurry pumps connected in series and each having a pressurerating, an inlet and an outlet, the first pump inlet operativelyconnected to the steaming vessel, the first pump outlet operativelyconnected to the second pump inlet, and the second pump having a higherpressure rating than the first pump. The slurry pumps may be helicalscrew centrifugal pumps, double-piston solids pumps, or other similarconventional pumping devices that are capable of pressurizing a slurryhaving a relatively high percentage of solids to (in one or more stages)a pressure of at least about 5 bar gauge. The pressurizing andtransferring may also be effected by an one or more eductors, ofconventional construction, driven by a pressurized fluid supply, such assupplied by conventional centrifugal pump.

[0009] One typical unit of measure that indicates the relative amount ofsolids in a slurry containing solids and liquid is the “liquid-to-solidsratio”. In this application, this ratio is the ratio of the volume ofliquid being transferred to the volume of cellulose, or wood, materialbeing transferred. Typical conventional centrifugal liquid pumps arelimited to pumping liquid having a solids content of at most 3%. This 3%solids content corresponds to a liquid-to-solids ratio of about 33. Inthe slurry pumps of this invention, the liquid-to-solids ratio of theslurry being pumped is typically between 2 and 10, preferably between 3and 7, and most preferably between 3 and 6. In other words, the slurrypumps of this invention transfer slurries having a much greater solidscontent than can be handled by a conventional pump.

[0010] A liquid return line may be provided from the top portion of thetreatment vessel, containing liquid separated from the slurry at the topof the treatment vessel (preferably a continuous digester). The returnline may be operatively connected to an inlet or outlet of one of theslurry pumps, either directly or indirectly. Preferably the liquidreturn line is connected to a pressure reduction means for reducing thepressure of liquid in the return line before the liquid passes to theinlet or outlet of the slurry pump. The pressure reduction means maytake a variety of forms, such as a flash tank and/or a pressure controlvalve in the return line, or other conventional structures foreffectively reducing the pressure of liquid in a line while notadversely affecting the liquid. Where a flash tank is utilized theliquid outlet from the flash tank is connected to the inlet to the firstslurry pump, and the steam produced by the flash tank may be used in thesteaming vessel.

[0011] Alternatively, the pressure reduction may be effected, or evenavoided, by using an eductor which uses the pressurized return lineliquor as its source of pressurized fluid. An eductor may be used inplace of or in conjunction with one or more of the slurry pumps, orother devices, to transfer slurry to the digester.

[0012] A conventional chute, as well as other optional components, ispreferably connected between the steaming vessel and the at least oneslurry pump, the steaming vessel being located above the chute and thechute above the at least one slurry pump. The at least one slurry pumpis typically located a distance at least 30 feet (about 10 meters) belowthe top of the digester, and typically more than about 50 feet (about 15meters) below.

[0013] When the high pressure transfer device is eliminated it isdesirable to utilize other mechanisms to retain one of the functions ofthe high pressure transfer device, namely providing pressure reliefprevention should an aberrant condition occur, the high pressuretransfer device typically preventing backflow of liquid from thedigester into the feed system. Pressure relief preventing meansaccording to the present invention are preferably distinct from the atleast one slurry pump, although under some circumstances the inlets toor outlets from the slurry pumps may be constructed in a manner so as toprovide pressure relief prevention. The pressure relief preventing meansmay comprise an automatic isolation valve in each of the slurry conduitstransferring slurry from the pumps to the top of the treatment vesseland the return line from the treatment vessel, a conventional controllerbeing provided connected to the isolation valves and operating theisolation valves in response to the pressure sensed by a pressure sensorassociated with the slurry conduit feeding slurry to the top of thetreatment vessel. The pressure relief preventing means may also comprisea check valve in the slurry conduit, and/or a variety of other valves,tanks, sensors, controllers, or like fluidic, mechanical, or electricalcomponents which can perform the pressure relief preventing function.

[0014] The system may also comprise means for augmenting the flow ofliquid to the inlet to the second slurry pump, or to any pump ortransfer device, such as a liquid line having liquid at a pressure belowthe pressure at the second slurry pump inlet, a conduit between theliquid line and the inlet, and a liquid pump in the conduit. The liquidline may be the return line from the treatment vessel, and the conduitmay be connected directly to the return line. The liquid return line maybe connected to a flash tank as described above, and the conduit may beconnected to the flash tank liquid outlet.

[0015] According to another aspect, a method of feeding comminutedcellulosic fibrous material to the top of a treatment vessel isprovided. The method comprises the steps of: (a) Steaming the materialto remove air therefrom and to heat the material. (b) Slurrying thematerial with a cooking liquor to produce a slurry of liquid andmaterial. And, (c) pressurizing the slurry to a pressure of at leastabout 5 bar gauge at a location below the top of the treatment vessel(e.g. at least thirty feet below, preferably at least fifty feet below),and transferring pressurized material to the top of the treatmentvessel, the pressurizing step consisting of acting on the slurry withone or more high pressure slurry pumps.

[0016] The method may comprise the further steps of: (d) returningliquid separated from the slurry at the top of the treatment vessel tothe at least one pump; and (e) sensing the pressure of the slurry whilebeing transferred to the top of the treatment vessel, and shutting offthe flow of slurry to the top of the treatment vessel and the return ofliquid from the top of the vessel if the sensed pressure drops below apredetermined value. There also may be the step (f) of flashing theliquid while returning in the practice of step (d) to produce steam, andusing the steam in the practice of step (a).

[0017] In an additional embodiment, the concept of transferring a slurryof chips is extended back to the point where chips are introduced to themill, that is, the Woodyard. Conventional pulp mills receive theirsupply of cellulose material, typically hardwood and softwood but otherforms of cellulose material as described above may be handled, invarious forms. These include as sawdust, as chip, as logs, as longde-limbed trees (that is, “long wood”), or even as complete trees (thatis, “whole trees”). Depending upon the source of cellulose of the “woodsupply”, the wood is typically reduced to chip form so that it can behandled and treated in a pulping process. For example, devices known as“chippers” reduce the long-wood or logs to chips that are typicallystored in open chip piles or chip silos. This receipt, handling, andstorage of the chips is performed in an area of the pulp mill referredto as the “woodyard”. From the Woodyard the chips are typicallytransferred to the pulp mill proper to initiate the pulping process.

[0018] In conventional Woodyards, the chips are stored in silos fromwhich the chips are discharged, typically by means of a rotating orvibrating silo discharge device, to a conveyor. This conveyor istypically a belt-type conveyor which receives the chips and transfersthem to the pulping treatment vessels. Since the Woodyard is typicallyat a distance from the pulping vessels, this conveyor is typically long.Such conveyors may have a length of up to one-half mile. In addition,treatment systems that do not employ the Lo-Level™ feeding system, asmarketed by Ahlstrom Machinery and described in U.S. Pat. Nos.5,476,572, 5,622,598, 5,635,025 and 5,766,416, require that the conveyorbe elevated, typically to a height of at least 100 feet, in order tofeed the chips to the inlet of the first pulping vessel. Theseconveyers, and the structures that support them, are very expensive andcontribute a significant cost to the cost of a digester feed system.

[0019] In another embodiment, the concept of transferring a slurry ofchips is extended back to the Woodyard. A preferred embodiment of thisinvention consists of a method of transferring comminuted cellulosicfibrous material to a pulping process, consisting of the followingsteps: (a) Introducing untreated chips to a first vessel. (b)Introducing slurrying liquid to the first vessel to create a slurry ofmaterial and liquid. (c) Discharging the slurry from the vessel to theinlet of at least one pressurizing and transferring device. (d)Pressurizing the slurry in the pressurizing and slurrying device andtransferring the slurry to a treatment vessel.

[0020] The first vessel is typically a chip storage silo or bin. Thisbin preferably has a discharge having one-dimensional convergencewithout agitation or vibration, such as a DIAMONDBACK® bin as describedin U.S. Pat. No. 5,000,083, though agitation or vibration may be used.This bin may also have two or more outlets which feed two or moretransfer devices. This vessel may also be operated at superatmosphericpressure, for example at 0.1 to 5 bar. If the vessel is operated atsuperatmospheric pressure some form of pressure isolation device must belocated at the inlet of the vessel to prevent the release of pressure.This device may be a star-type isolation device, such as a Low-pressureFeeder or Air-lock Feeder as sold by Ahlstrom Machinery, or a screw-typefeeder having a sealing capacity as described in U.S. Pat. No.5,766,416.

[0021] The slurrying liquid may be any source of liquid available in thepulp mill, including fresh water, steam condensate, kraft white, black,or green liquor or sulfite liquor or any other pulping-related liquid.This liquid may be a heated fluid, for example, hot water or steam,having a temperature of between 50 and 100° C. If the vessel is apressurized vessel, liquid temperatures of over 100° C. may be used.Though not essential, this liquid may contain at least some activepulping chemical, for example, sodium hydroxide (NaOH), sodium sulfide(Na2S), polysulfide, anthraquinone or their equivalents or derivativesor surfactants, enzymes or chelates, or combinations thereof.

[0022] The pressurizing and transferring device of steps (c) and (d) ispreferably a slurry pump, or pumps, but many other pressurizing andtransferring devices may be used such as the piston-type solids pump ora high-pressure eductor. Preferably, more than one pressurizing andslurrying pump is used to transfer the slurry. These may be two or moreslurry pumps, or any combination of slurry pump, piston-type pump, oreductor. This transfer system may also include one or more storage orsurge tanks as well as transfer devices. Preferably, the one or moretransfer devices include at least one device having de-gassingcapability so that undesirable air or other gases may be removed fromthe slurry. Also, during transfer, the chips may be exposed to some formof treatment, for example, de-aeration or impregnation with a liquid,preferably a liquid containing pulping chemicals, such as thosedescribed above. The slurry may also be exposed to at least one pressurechange or fluctuation during transfer, for example, such that thepressure of the slurry is varied from a first pressure to a second,higher pressure, and then optionally to a third pressure which is lowerthan the second pressure. As described in U.S. Pat. Nos. 4,057,461 and4,743,338 varying the pressure of a slurry of chips and liquor improvesthe impregnation of the chips by the liquor. This pressure pulsation maybe achieved by varying the outlet pressure of a set of transfer devicesin series, or by controlled depressurization of the slurry betweenpumping.

[0023] In another embodiment, the material need not encounter liquid inthe vessel, but may have liquid first introduced to it by means of aneductor located in or below the outlet of the vessel. This liquid ispreferably pressurized so that the material and liquid form apressurized slurry of material and liquid.

[0024] The treatment vessel of step (d) may typically be a steamingvessel as described above, preferably a DIAMONDBACK® steaming vessel.The vessel may also be a storage or surge tank in which the material maybe stored prior to treatment. Since the transfer process may requireexcess liquor that is not needed during treatment or storage, some formof de-watering device may be located between the transfer device and thetreatment vessel. One preferred dewatering device is a Top Separator, assold by Ahlstrom Machinery. This Top Separator may be a standard type oran “inverted” Top Separator. This device may be an externalstand-alone-type unit or one that is mounted directly onto the treatmentvessel. An In-line Drainer, also sold by Ahlstrom Machinery, may also beused for the dewatering device. Preferably, the liquid removed from theslurry by means of the de-watering device is returned to the firstvessel or to the transfer devices to act as the slurring liquid. Thisliquid may also be used where ever needed in the pulp mill. This liquidmay be heated or cooled as desired. For example, this liquid may beheated by passing it in indirect heat exchange relationship with anyheated liquid stream, for example, a waste liquid stream having atemperatures greater than 50° C. This liquid will also typically bepressurized using one or more conventional centrifugal liquid pumps.

[0025] In one preferred embodiment the treatment vessel of step (d) is asteaming vessel which feeds one or more transfer devices as describedabove. Though this system is preferably used in conjunction with a feedsystem not having a conventional High-pressure Feeder, this system mayalso be used with a feed system having a High-pressure Feeder.

[0026] The method and apparatus for feeding chips from a distantlocation, for example, a Woodyard, to a pulping process is not limitedto chemical pulping processes, but may be used in any pulping process inwhich comminuted cellulosic fibrous material is conveyed from onelocation to another. The pulping processes that this invention isapplicable to include all chemical pulping processes, all mechanicalpulping processes, and all chemi-mechanical pulping orthermal-mechanical pulping processes, for either batch or continuoustreatment.

[0027] According to another aspect there is provided a method of feedingwood chips to the top of a treatment vessel comprising the steps of: (a)Steaming the wood chips to remove air therefrom and to heat thematerial. (b) Slurrying the wood chips with a cooking liquor to producea slurry of liquid and material. (c) Pressurizing the slurry to apressure of at least about 5 bar gauge at a location at least thirtyfeet below the top of the treatment vessel and transferring pressurizedwood chips to the top of the treatment vessel, the pressurizing stepconsisting essentially of acting on the slurry with one or more highpressure slurry pumps. And, (d) during the practice of the transferringstep (c), treating the wood chips with polysulfide, anthraquinone ortheir equivalents or derivatives, surfactants, enzymes, chelants, orcombinations thereof.

[0028] Where the treatment vessel is upstream of a continuous or batchdigester, step (c) is typically practiced downstream of the treatmentvessel. There may also be the further step (e), before the continuous orbatch digester and substantially immediately after steps (a) and (b), ofpressurizing the slurry at a location at least 30 feet below the top ofthe digester, and transferring pressurized wood chips to the top of thedigester, the pressurizing step consisting of acting on the slurry withone or more high pressure slurry pumps. There may also be the step ofreturning liquid removed from the digester to the treatment vessel, andadjusting the temperature of the liquid while returning it to thetreatment vessel. The step of removing liquid from the treatment vesseltypically takes place at the top of the treatment vessel.

[0029] The method may also comprise the further step of returning liquidfrom downstream of the treatment vessel to the treatment vessel, andadjusting the temperature of the liquid, and the step of adjusting thetemperature of the liquid may take place by passing the liquid throughan indirect heat exchanger. The method may also comprise the furtherstep of returning liquid separated from the slurry at the top of thedigester to the one or more slurry pumps, pressurizing the slurry totransfer it to the digester, and adjusting the temperature of theremoved liquid during recirculation.

[0030] The system and method herein not only reduce the size and cost ofthe system for transferring comminuted cellulosic fibrous material, butif the comminuted cellulosic fibrous material is treated duringtransfer, the number and size of the formal treatment vessels may bereduced. For example, this system may eliminate the need forconventional pretreatment or impregnation vessels prior to the digester.This system also has the potential for improving the over-all energyeconomy of the pulp mill. This and other aspects of the invention willbecome manifest upon review of the detailed description and figurebelow.

[0031] According to another aspect a method of treating comminutedcellulosic fibrous material using at least first and second seriesconnected pumps, and at least first and second in series stations eachwith a solids/liquid separator is provided. The method comprises thesteps of: (a) Pumping a slurry of comminuted cellulosic fibrous materialusing the series connected pumps. (b) Separating some liquid from theslurry at each station to substantially isolate liquor circulations andstreams, and to recirculate removed liquid from at least one of thestations to upstream of one of the pumps. And (c) adding chemicals tothe slurry upstream of each of the pumps, the chemicals including atleast some chemical selected from the group consisting essentially ofsodium hydroxide, sodium sulfate; polysulfide, anthraquinone, or theirequivalents or derivatives; surfactants, enzymes, or chelants; orcombinations thereof; so that pre-treatment of the material occursduring transfer of the material from each pump to each station.

[0032] There may be the further step of degassing the slurry at at leastone of the stations. At least first, second and third series connectedpumps and stations may be provided; and there may also be the furthersteps of: (d) Circulating liquid removed from the third station to alocation upstream of the second pump, and (e) circulating liquid removedform the second station to a location upstream of the first pump (step(d) may be practiced downstream of the first station). There may also bethe further step of passing the removed liquid, during the practice ofat least one of steps (d) and (e), through a heat exchanger to changethe temperature thereof. For example, the temperature of the removedliquid may be increased or decreased by from about 1 to about 10° C.,depending upon the volume of the liquid and the amount of heating orcooling available.

[0033] Step (c) may be practiced by adding a different chemical, orcombination of chemicals, upstream of each pump, so that significantlydifferent treatments of the material of the slurry take place duringtransfer of the slurry from each pump to its associated station. Step(a) may be practiced to pressurize the slurry to a pressure of at least5 bar. Also, there may be the further step of removing liquid from atleast one of the stations through an eductor (also known as an ejector)instead of a flash tank and/or control valve.

[0034] According to another aspect of this invention, one treatment thatcan be used during the transfer of comminuted cellulosic fibrousmaterial is the removal of metal ions. It is recognized in the art thatthe presence of certain metallic compounds or ions, for example, thosecontaining iron, calcium, manganese, and others, can interfere withpulping and bleaching reactions or can precipitate as undesirable“scale” on the treatment equipment. It is also known the metal contentof the cellulose material can be reduced by exposing the material toacidic liquids which can dissolve metal compounds or ions or to acidicto slightly alkaline conditions in the presence of a chelating agent(also known as a sequestering agent) which combine with certain metalsand make them more easily isolated and removed, for example, by washing.According to the present invention, these deleterious metal-containingcompounds and ions are removed from the cellulose material prior to thecooking process and bleaching process so that these metals do notinterfere with these processes nor form scale on the equipment used toeffect these processes.

[0035] According to this aspect of the invention, there is provided amethod of treating a slurry of comminuted cellulosic fibrous materialusing at least first and second series connected pumps, and at leastfirst and second in-series stations, each with a solids/liquidseparator, in which the metal content of the material is reduced. Themethod comprises: (a) Pumping a slurry of comminuted cellulosic fibrousmaterial using the series connected pumps. (b) Separating some liquidfrom the slurry at each station to substantially isolate liquorcirculations and streams, and to recirculate removed liquid from atleast one of the stations to upstream of one of the pumps. And (c)adding chemicals which dissolve or sequester metal containing compoundsto the slurry at or upstream of at least one of the pumps, the chemicalsincluding at least one chemical selected from the group consistingessentially of acids, chelating agents, and combinations thereof, sothat at least some of the deleterious metals (e.g. at least about 10%,preferably about 20%-80%) present in the material prior to treatment areremoved from the material.

[0036] There may further be (d) removing at least some of the liquidfrom the slurry during (a) or (b) to purge at least some (e.g. at leastabout 10%, preferably about 20%-80%) of the metal containing compoundsfrom the liquor circulations. This liquid may be removed in a liquorseparating device, for example, a conventional Top Separator or In-linedrainer, or the liquid may simply be removed via a branch conduit in thecirculation line. Also (d) may also be practiced at substantially thesame time as and using substantially the same equipment in which (b) ispracticed. There may also further be (e) introducing liquid to thecirculation to substantially replace the liquid removed in (d). Theliquid introducing procedure (e) may be practiced substantiallyimmediately downstream of where (d) is practiced or elsewhere in thesystem. Also (e) may be practiced substantially in conjunction with (c)so that replacement liquid is introduced substantially with thetreatment chemical.

[0037] This invention is preferably practiced before a further procedure(f) of treating the material with an alkaline liquid and (g) digestingthe material in an alkaline digestion process; preferably (a)-(e) arepracticed substantially immediately prior to (f) and (g). The alkalineliquid may comprise, for example, kraft white, green, or black liquor(which may contain yield or strength enhancing additives as describedabove). Thus, in a preferred embodiment of the invention, the chemicalused to effect (c) is introduced at or upstream of the first pump andthe chemical used to effect (f) is introduced at or upstream of thesecond pump.

[0038] According to another aspect a method of treating comminutedcellulosic fibrous material is provided comprising the steps of: (a)Pumping a slurry of comminuted cellulosic fibrous material using the atleast first and second series connected pumps. (b) Separating someliquid from the slurry at each station to substantially isolate liquorcirculations and streams, and to recirculate removed liquid from atleast one of the stations to upstream of one of the pumps. (c) Addingtreatment chemical to the slurry upstream of at least one of the pumpsso that pre-treatment of the material occurs during transfer of thematerial from that pump to its associated station. And (d) circulatingliquid removed form the second station to a location upstream of thefirst pump. Where at least first, second and third pumps and stationsare provided, there is the further step (e) of circulating liquidremoved from the third station to a location upstream of the secondpump. The details of the steps, or additional steps, may be as set forthabove.

[0039] According to one aspect of the invention there is provided asystem for producing chemical cellulose pulp from comminuted fibrouscellulose material, comprising: A steaming vessel in which comminutedfibrous cellulose material is steamed to remove the air therefrom. Asuperatmospheric pressure vertical treatment vessel having an inlet fora slurry of comminuted cellulose fibrous material at a top portionthereof and an outlet at a bottom portion thereof. Pressurizing transfermeans for pressurizing a slurry of material from the steaming vessel andtransferring it to the treatment vessel inlet, the pressurizing transfermeans consisting of one or more high pressure slurry pumps, each havingan inlet and outlet, located below the top portion of the treatmentvessel. And means for circulating liquid from the outlet of at least onethe high pressure slurry pump to the inlet thereof.

[0040] The recirculation means may be conduits and associatedconnections to other components, although any conventional structureswhich allow or provide this recirculation may be utilized includingvalves (in or apart from the conduits), tanks, ejectors, pumps, ducts,heat exchangers, or the like.

[0041] The system preferably further comprises a liquid return line fromthe top portion of the treatment vessel, the return line operativelyconnected to an inlet or outlet of one of the slurry pumps.

[0042] The system may also comprise a heat exchanger located in thereturn line, which preferably is a liquid-to-liquid indirect heatexchanger. While the heat exchanger may be used for cooling or heatingliquid in a return line preferably it is connected to a source of coolliquid and cools the liquid in the return line, so that it is below thepoint where it will flash in the system.

[0043] The system may further comprise a slurrying vessel having aninlet operatively connected to the steaming vessel and an outletoperatively connected to the inlet of the one or more slurry pumps; thesystem may still further comprise a liquid return line from the topportion of the treatment vessel, the return line operatively connectedto the slurry vessel, and the heat exchanger in the return line.

[0044] Preferably the at least one pump comprises at least two pumps,and each of the pumps has a recirculation means as described above. Therecirculation means may comprise a first valve in a recirculationconduit, and a second valve between the pump outlet and the treatmentvessel, and preferably each of the pumps has a recirculation means asdescribed above associated therewith.

[0045] The treatment vessel may be a first treatment vessel, and thesystem may further comprise a second treatment vessel. The main conduitis connected to the outlet of the pump (or the last in a series ofpumps), and a flow splitter is provided having an inlet and at least twooutlets. The main conduit is connected to the flow splitter inlet, andone of the flow splitter outlets is connected to the first treatmentvessel, and another outlet to the second treatment vessel. The firsttreatment vessel may also include two or more inlets and the at leasttwo or more outlets of the flow splitter may be connected to the two ormore inlets of the first vessel. The flow splitter may comprise achamber having a substantially triangular shaped static baffle platearrangement with a triangle apex substantially aligned with the inlet.

[0046] According to another aspect of the invention there is provided amethod of feeding cellulosic material to the top of a treatment vesselcomprising the steps of: (a) Steaming the material to remove airtherefrom and to heat the material. (b) Slurrying the material with acooking liquor to produce a slurry of liquid and material. And (c)pressurizing the slurry at a location at least thirty feet below the topof the treatment vessel and transferring pressurized material to the topof the treatment vessel, the pressurizing step consisting of acting onthe slurry with two or more high pressure slurry pumps.

[0047] The method may also comprise (d) establishing a recirculationloop between each pump outlet and inlet during startup. For example,there may be a first valve in the recirculation loop and a second valvebetween each pump outlet and the treatment vessel, in which case (d) ispracticed to open the first valve and at least partially (e.g.completely) close the second valve during startup. Then the method mayfurther comprise (e) after startup closing the first valve and openingthe second valve. The method may also further comprise returning theliquid from the treatment vessel to one of the pump inlets (preferably afirst in-series pump) and partially cooling the cooling liquid (e.g.with an indirect liquid-to-liquid heat exchanger) so that the returningliquid has a temperature below the point it will flash during handling.

[0048] The method may be practiced further utilizing at least a secondtreatment vessel or a first treatment vessel having two or more inlets,and may further comprise statically splitting the flow of slurry fromthe outlet of the last of the pumps to direct part of the flow to eachtreatment vessel or the inlets of the first treatment vessel.

[0049] According to another aspect of the present invention there isprovided a method of feeding comminuted cellulosic fibrous material tothe top of a treatment vessel, comprising: (a) Steaming the material toremove air therefrom and to heat the material. (b) Slurrying thematerial with a cooking liquor to produce a slurry of liquid andmaterial; (c) Pressurizing the slurry at a location at least thirty feetbelow the top of the treatment vessel and transferring pressurizedmaterial to the top of the treatment vessel, said pressurizing stepconsisting of acting on the slurry with one or more high pressure slurrypumps. And (d) establishing a recirculation loop between the pump outletand inlet during startup. A first valve may be provided in therecirculation loop and a second valve between the pump outlet and thetreatment vessel; and (d) may be practiced to open the first valve andat least partially close the second valve during startup; and the methodmay further comprise (e) after startup closing the first valve andopening the second valve. Cooling and returning liquid, and flowsplitting, may also be practiced, as described above.

[0050] According to another aspect of the present invention there isprovided a static flow splitter comprising: A static chamber. An inletand at least two outlets connected to the chamber. And a substantiallytriangular shaped static baffle plate arrangement may be located withinthe chamber and have a triangle apex substantially aligned with theinlet.

[0051] It is the primary object of the present invention to provide asimple and effective system and method for feeding cellulose slurry to atreatment vessel, and also while achieving enhanced operability andmaintainability. This and other objects of the invention will becomeclear from an inspection of the detailed description of the inventionand from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0052]FIG. 1 illustrates a typical prior art system for feeding a slurryof comminuted cellulosic fibrous material to a continuous digester;

[0053]FIG. 2 illustrates another prior at system for feeding a slurry ofcomminuted cellulosic fibrous material to a continuous digester;

[0054]FIG. 3 illustrates one typical embodiment of a system for feedinga slurry of comminuted cellulosic fibrous material to a continuousdigester according to this invention;

[0055]FIGS. 4 and 5 illustrate two other embodiments of systemsaccording to the invention;

[0056]FIG. 6 is a schematic representation of another system that may beused for practicing a method according to the invention;

[0057]FIG. 7 is a schematic illustration of another typical system forfeeding a slurry of comminuted cellulosic fibrous material to adigester, according to the invention;

[0058]FIG. 8 is a side view, with a portion of the near wall of the flowchamber cut away so as to illustrate the interior thereof, of anexemplary flow splitter according to the present invention; and

[0059]FIGS. 9 and 10 are top and end views of the flow splitter of FIG.8.

DETAILED DESCRIPTION OF THE DRAWINGS

[0060] Though the systems shown and described in FIGS. 1-3 arecontinuous digester systems, it is understood that the method and systemof the present invention can also be used to feed one or more batchdigesters, or an impregnation vessel connected to a continuous digester.The continuous digesters shown and which may be used with this inventionare preferably KAMYR® continuous digesters, and may be used for kraft(i.e., sulfate) pulping, sulfite pulping, soda pulping or equivalentprocesses. Specific cooking methods and equipment that may be utilizedinclude the MCC®, EMCC®, and Lo-Solids® processes and digesters marketedby Ahlstrom Machinery Inc. Strength or yield retaining additives such asanthraquinone, polysulfide, or their equivalents or derivatives may alsobe used in the cooking methods utilizing the present invention.

[0061]FIG. 1 illustrates one typical prior art system 10 for feeding aslurry of comminuted cellulosic fibrous material, for example, softwoodchips, to the top of a continuous digester 11. Digester 11 typicallyincludes one liquor removal screen 12 at the inlet of the digester 13for removing excess liquor form the slurry and returning it to feedsystem 10. Digester 11 also includes at least one liquor removal screen14 for removing spent cooking liquor during or after the pulpingprocess. Digester 11 also typically includes one or more additionalliquor removal screens (not shown) which may be associated with cookingliquor circulation, such as an MCC®, EMCC® digester cooking circulation,or a Lo-Solids® digester circulation having a liquor removal conduit anda dilution liquor addition conduit. Cooking liquor, for example, kraftwhite, black, or green liquor, may be added to these circulations.Digester 11 also includes an outlet 15 for discharging the chemical pulpproduced which may be passed on to further treatment such as washing orbleaching.

[0062] In the prior art feed system 10 shown in FIG. 1, comminutedcellulosic fibrous material 20 is introduced to chip bin 21. Typically,the material 20 is softwood or hardwood chips but any form of comminutedcellulosic fibrous material, such as sawdust, grasses, straw, bagasse,kenaf, or other forms of agricultural waste or a combination thereof,may be used. Though the term “chips” is used in the following discussionto refer to the comminuted cellulosic fibrous material, it is to beunderstood that the term is not limited to wood chips but refers to anyform of the comminuted cellulosic fibrous materials listed above, or thelike.

[0063] The chip bin 21 may be a conventional bin with vibratorydischarge or a DIAMONDBACK® steaming vessel, as described in U.S. Pat.No. 5,500,083 and sold by Ahlstrom Machinery Inc., having no vibratorydischarge but having an outlet exhibiting one-dimensional convergenceand side relief. The bin 21 may include an airlock device at its inletand a means for monitoring and controlling the level of chips in the binand a vent with an appropriate mechanism for controlling the pressurewithin the bin. Steam, either fresh or steam produced from theevaporation of waste liquor (i.e., flashed steam), is typically added tobin 21 via one or more conduits 22.

[0064] The bin 21 typically discharges to a metering device, 23, forexample a Chip Meter sold by Ahlstrom Machinery, but other forms ofdevices may be used, such as a screw-type metering device. The meteringdevice 23 discharges to a pressure isolation device 24, such as aLow-Pressure Feeder sold by Ahlstrom Machinery. The pressure isolationdevice 24 isolates the pressurized horizontal treatment vessel 25 fromthe essentially atmospheric pressure that exists above device 24.

[0065] Vessel 25 is used to treat the material with pressurized steam,for example steam at approximately 10-20 psig. The vessel 25 may includea screw-type conveyor such as a Steaming Vessel sold by AhlstromMachinery. Clean or flashed steam is added to the vessel 25 via one ormore conduits 28.

[0066] After treatment in vessel 25, the material is transferred to ahigh-pressure transfer device 27, such as a High-Pressure Feeder sold byAhlstrom Machinery. Typically, the steamed material is transferred tothe feeder 27 by means of a conduit or chute 26, such as a Chip Chutesold by Ahlstrom Machinery. Heated cooking liquor, for example, acombination of spent kraft black liquor and white liquor, is typicallyadded to chute 26 via conduit 29 so that a slurry of material and liquoris produced in chute 26.

[0067] If the prior art system of FIG. 1 does employ a DIAMONDBACK®steaming vessel as disclosed in U.S. Pat. No. 5,000,083, which producesimproved steaming under atmospheric conditions, the pressurizedtreatment vessel 25 and the pressure isolation device 24 may be omitted.

[0068] The conventional High-Pressure Feeder 27 contains a low pressureinlet connected to chute 26, a low pressure outlet connected to conduit30, a high-pressure inlet connected to conduit 33, a high-pressureoutlet connected to conduit 34, and a pocketed rotor driven by avariable-speed electric motor and speed reducer (not shown). The lowpressure inlet accepts the heated slurry of chips from chute 26 into apocket of the rotor. A screen in the outlet, at 30, of the feeder 27retains the chips in the rotor but allows the liquor in the slurry topass through the rotor to be removed via conduit 30 and pump 31. As therotor turns the chips that are retained within the rotor are exposed tohigh pressure liquid from pump 32 via conduit 33. This high-pressureliquor slurries the chips out of the feeder and passes them to the topof digester 11 via conduit 34. Upon reaching the inlet of digester 11some of the excess liquor used to slurry the chips in conduit 34 isremoved from the slurry via screen 12. The excess liquor removed viascreen 12 is returned to the inlet of pump 32 via conduit 35. The liquorin conduit 35, to which fresh cooking liquor may be added, ispressurized in pump 32 and passed in conduit 33 for use in slurrying thechips out of feeder 27. The chips that are retained by the screen 12pass downwardly in the digester 11 for further treatment.

[0069] The liquor removed from feeder 27 via conduit 30 and pump 31 isrecirculated to the chute 26 above the feeder 27 via conduit 36, sandseparator 37, conduit 38, in-line drainer 39 and conduit 29. Sandseparator 37 is a cyclone-type separator for removing sand and debrisfrom the liquor. In-line drainer 39 is a static screening device whichremoves excess liquor from conduit 38 and passes it through conduit 39′and stores it in level tank 40. Liquor stored in tank 40 is returned tothe top of the digester via conduit 41, pump 42 (i.e., the Make-upLiquor Pump), and conduit 43. Fresh cooking liquor may also be added toconduits 41 or 43.

[0070]FIG. 2 illustrates another prior art system 110 for feeding chipsto a digester. This system uses processes and equipment described inU.S. Pat. Nos. 5,476,572, 5,622,598 and 5,635,025. This equipment andthe processes they are used to effect are collectively marketed underthe trademark Lo-Leve™ by Ahlstrom Machinery. The components in FIG. 2which are identical to those that appear in FIG. 1 are identified by thesame reference numbers. Those components which are similar or whichperform similar functions to those that appear in FIG. 1 have theirreference numbers that appear in FIG. 1 prefaced by the numeral “1”.

[0071] Similar to the system of FIG. 1, chips 20 are introduced tosteaming vessel 121 where they are exposed to steam introduced viaconduit 22. The vessel 121 discharges to metering device 123, and thento conduit 126, which is preferably a Chip Tube as sold by AhlstromMachinery. Cooking liquor is typically introduced to tube 126 viaconduit 55, similar to conduit 29 of FIG. 1. Since the vessel 121 ispreferably a DIAMONDBACK® steaming vessel as described in U.S. Pat. No.5,000,083, no pressure isolation device, 24 in FIG. 1, or pressurizedsteaming vessel 25 in FIG. 1, are needed in this prior art system. Asdisclosed in U.S. Pat. No. 5,476,572 instead of discharging the slurryof chips and liquor directly to feeder 27, a high-pressure slurry pump51 fed by conduit 50 is used to transport the chips to the feeder 27 viaconduit 52. The pump 51 is preferably a Hidrostal pump as supplied byWemco, or similar pump supplied by the Lawrence company. The chips thatare passed via pump 51 are transported to digester 11 by feeder 27 in amanner similar to what was shown and described with respect to FIG. 1.

[0072] In addition to using the pump 51 to pass the slurry to the feeder27, the system of FIG. 2 does not require the pump 31 of FIG. 1. Pump 51supplies the motive force for passing liquor through the feeder 27,through conduit 30, sand separator 37, in-line drainer 39, and conduit129 to liquor level tank 53.

[0073] The function of level tank 53 is disclosed in pending applicationSer. No. 08/428,302, filed on Apr. 25, 1995. The tank 53 ensures asufficient supply of liquor to the inlet of the pump 51, via conduit 54.This tank may also supply liquor to tube 126 via conduit 55. This liquortank 53 also allows the operator to vary the liquor level in the feedsystem such that, if desired, the liquor level may be elevated to themetering device 123 or even to the bin 121. This option is alsodescribed in pending application Ser. No. 08/354,005, filed on Dec. 5,1994.

[0074]FIG. 3 illustrates one preferred embodiment of a feed system 210that simplifies even further the prior art feeding systems shown inFIGS. 1 and 2. In the preferred embodiment shown in FIG. 3, thehigh-pressure transfer device, component 27 of FIGS. 1 and 2, has beeneliminated. Instead of transferring chips to the feeder 27 by means ofgravity in chute 26 of FIG. 1 or via pump 51 in FIG. 2, at least one,preferably two, high-pressure slurry pumps 251, 251′ are used totransport the slurry to the inlet of the digester 11. The components inFIG. 3 which are essentially identical to those that appear in FIGS. 1and 2 are identified by the same reference numbers. Those componentswhich are similar or which perform similar functions to those thatappear in FIGS. 1 and 2 have their reference numbers that appear inFIGS. 1 and 2 prefaced by the numeral “2”.

[0075] Similar to the procedure in FIGS. 1 and 2, according to theembodiment of FIG. 3, chips 20 are introduced to steaming vessel 221.The chips are preferably introduced by means of a sealed horizontalconveyor as disclosed in pending application Ser. No. 08/713,431, filedon Sep. 13, 1996. Also, the steaming vessel 221 is preferably aDIAMONDBACK® steaming vessel as described in U.S. Pat. No. 5,000,083 towhich steam is added via one or more conduits 22. The steaming vessel221 typically includes conventional level monitoring and controls aswell as a pressure-relief device (not shown). Vessel 221 dischargessteamed chips to metering device 223, which, as described above, may bea pocketed rotor-type device such as a Chip Meter or a screw-typedevice.

[0076] In one embodiment the metering device 223 discharges directly toconduit or chute 226. However, in an optional embodiment, a pressureisolating device, such as a pocketed rotor-type isolation device, shownin dotted line at 224, for example a conventional Low-pressure Feeder,may be located between metering device 223 and chute 226. Though withoutthe pressure-isolation device 224 the pressure in chute 226 isessentially atmospheric, with a pressure isolation device 224 thepressure in chute 226 may range from 1 to 50 psig, but is preferablybetween 5 to 25 psig, and most preferably between about 10 to 20 psig.Cooking liquor, as described above, is added to chute 226 (see line 226′in FIG. 3) so that a slurry of chips and liquor is produced in chute 226having a detectable level (not shown). The slurry in chute 226 isdischarged via radiused outlet 250 to the inlet of pump 251. Theintroduction of slurry to the inlet of pump 251 is typically augmentedby liquor flow from liquor tank 253 via conduit 254 as described inpending application Ser. No. 08/428,302.

[0077] Pump 251 is preferably a centrifugal high-pressure, helicalscrew, slurry pump, such as a “Hidrostal” pump supplied by Wemco of SaltLake City, Utah. The pump 251 may alternatively be a slurry pumpsupplied by the Lawrence Company of Lawrence, Mass. The pressure at theinlet to pump 251 may vary from atmospheric to 50 psig depending uponwhether a pressure isolation device 224 is used.

[0078] In the preferred embodiment illustrated in FIG. 3, the outlet ofpump 251 discharges to the inlet of pump 251′. Pump 251′ is preferablythe same type of pump as pump 251 but with the same or a higher pressurerating. If two pumps are used, the pressure produced in the outlet ofpump 251′ typically ranges from 150 to 400 psig (i.e., 345-920 feet ofwater, gauge), but is preferably between about 200 and 300 psig (i.e.,460-690 feet). If necessary, the liquor in the slurry in conduit 252 maybe augmented by liquor from tank 253 via conduit 56 and liquid pump 57.

[0079] Though the embodiment illustrated in FIG. 3 includes two pumps,only one pump, or even three or more pumps, in series or parallel, mayalternatively be used. In these cases, the discharge pressure from theone pump, or from the last pump, is preferably the same as the dischargepressure from pump 251′ above.

[0080] The pressurized, typically heated, slurry is discharged from pump251′ to conduit 234. Conduit 234 passes the slurry to the inlet ofcontinuous digester 11. Excess liquor in the slurry is removed viascreen 12 as is conventional. The excess liquor is returned to the feedsystem 210 via conduit 235, preferably to liquor tank 253 for use inslurrying in conduit 250 via conduit 254. The liquor in conduit 235 maybe passed through a sand separator 237 if desired. This sand separator237 may be designed for pressurized or unpressurized operation dependingupon the mode of operation desired.

[0081] Unlike the prior art systems employing a High-Pressure Feeder (27in FIGS. 1 and 2) which uses the pressure of the liquor returned viaconduit 35 as an integral part of the method of slurrying from theHigh-Pressure Feeder to the digester 11, it is not essential for theoperation of the present invention that the pressurized recirculation235 be returned to the inlet of the pumps 251, 251′. The energyavailable in the pressure of the flow in line 235 may be used wherevernecessary in the pulp mill. However, in a preferred embodiment, thepresent invention does utilize the pressure available in conduit 235 tominimize the energy requirements of pumps 251 and 251′ as much aspossible.

[0082] How the pressure in return line 235, typically about 150 to 400psig is used depends upon the mode of operation of the feed system 210.If vessel 226 is operated in an unpressurized-essentiallyatmospheric-mode, the pressurized liquor returned in conduit 235 must bereturned to essentially atmospheric pressure before being introduced toconduit 250. One means of doing this is to use a pressure control valve58 and a pressure indicator 59 in conduit 235. The opening in valve 58is controlled such that a predetermined reduced pressure exists in line235 downstream of valve 58. In addition, the liquor tank 253 may bedesigned so that it acts as a “flash tank” so that the hot pressurizedliquor in conduit 235 is rapidly evaporated to produce a source of steamin vessel 253. This steam can be used, among other places, in vessel 221via conduit 60. However, instead, in a preferred embodiment, thepressurized liquor in conduit 235 is used to augment the flow out ofpump 251′, for example via conduit 61 and pump 62. The pressure inconduit 235 may also be used to augment the flow between pumps 251 and251′ in conduit 252 via conduit 63, with or without pump 64 (a checkvalve may in some cases be used in place of or in addition to each ofpumps 62, 64). By re-using some of the pressure available in line 235,some of the energy requirements of pumps 251 and 251′ may be reduced.

[0083] Also, the heat of the liquor in line 235 can also be passed inheat-exchange-relationship with one or more other liquids in the pulpmill that need to be heated.

[0084] The pressurizing and transferring of pumps 251 and 251′ mayinstead by effected by a conventional eductor, for example, an eductormanufactured by Fox Valve Development Corporation. Or pumps 251, 251′may be used in conjunction with an eductor for increasing the pressurein the inlet or outlet of the pumps. An eductor may also be used as ameans of introducing liquid to the chips. For example, an eductor may belocated in the outlet of or beneath vessel 226 and liquid firstintroduced to the chips by means of this eductor. The eductor maycomprise a venturi-type orifice in one or more conduits 250, 252, and234 into which a pressurized stream of liquid is introduced. Thispressurized liquid may be obtained from any available source but ispreferably obtained from conduit 235, upstream of valve 58. An exemplaryeductor is shown schematically at 70 in FIG. 3.

[0085] The pumps 251 and 251′ need not be centrifugal pumps but may beany other form of slurry transfer device that can directly act on topressurize and transfer a slurry of chips and liquor from the outlet ofvessel 226 to the inlet of digester 11. For instance, a solids pump astypically used in the mining industry may be used; for example, adouble-piston solids pump such as the KOS solids pump sold byPutzmeister, or any other similar conventional pumping device may beused.

[0086] One function of the prior High-Pressure Feeder 27 of FIGS. 1 and2 is to act as a shut-off valve to prevent possible escape of thepressure in the equipment and transfer conduits, for example, conduits34 and 35 of FIG. 1, should any of the feed components malfunction orfail. In the feed system 210 according to the present invention,alternative means are provided to prevent such release of pressure dueto malfunction or failure. For example, FIG. 3 illustrates a one-way(check) valve 65 in conduit 234 to prevent pressurized flow fromreturning to pump 251 or 251′. In addition, conventional automatic (e.g.solenoid operated) isolation valves 66 and 67 are located in conduits234 and 235, respectively, to isolate the pressurized conduits 234, 235from the rest of the feed system 210. In one preferred mode ofoperation, a conventional pressure switch 68 is located downstream ofpump 251′ in conduit 234. The switch 68 is used to monitor the pressurein line 234 so that should the pressure deviate from a predeterminedvalue, the conventional controller 69 will automatically isolatedigester 11 from feed system 210 by automatically closing valves 66 and67. These valves may also be automatically closed when a flow directionsensor detects a reversal of flow in conduit 234.

[0087] While the pressure release preventing means 65-69 described aboveis preferred, other arrangements of valves, sensors, indicators, alarms,or the like may comprise the pressure release preventing means as longas such arrangements adequately perform the function of preventingsignificant depressurization of the digester 11.

[0088] While the system 210 is preferably used with a continuousdigester 11, it also may be used with other vertical superatmospheric(typically a pressure of at least about 10 bar gauge) treatment vesselshaving a top inlet, such as an impregnation vessel or a batch digester.

[0089]FIG. 4 illustrates a further embodiment in which the concept oftransferring chips is extended from the feed system of a digester to theWoodyard of a pulp mill. FIG. 4 illustrates a system 510 for feedingcomminuted cellulosic fibrous material to a pulping process. It consistsof a subsystem 410 for introducing chips from the Woodyard to system 510and a subsystem 310 for treating and feeding chips to digester 11.Subsystem 310 is essentially identical to the system 210 shown in FIG.3.

[0090] Again, the components in FIG. 4 which are identical to those thatappear in FIGS. 1-3 are identified by the same reference numbers. Thosecomponents which are similar or which perform similar functions to thosethat appear in FIG. 1-3 have their reference numbers that appear in FIG.1 prefaced by the numeral “3”.

[0091] The Woodyards of conventional pulp mills receive their woodsupply in various forms as described above. Typically, the wood, orother comminuted cellulosic fibrous material, is converted to chip likeform and stored either in open chip piles or in chip storage silos. InFIG. 4 the chip supply is shown as chip pile 80. In a preferredembodiment of this invention the chips from pile 80 or some otherstorage vessel are conveyed by conventional means, e.g., a conveyor orfront-end loader (not shown), and introduced 20 to vessel 81. Thisvessel may be a DIAMONDBACK® vessel or any other conventional storagevessel. Vessel 81 may be operated at superatmospheric pressure, forexample at 0.1 to 5 bar. If the vessel is operated at superatmosphericpressure, some form of pressure isolation device (not shown) may belocated at the inlet of the vessel to prevent the release of pressure.This device may be a star-type isolation device, such as a Low-pressureFeeder or Air-lock Feeder as sold by Ahlstrom Machinery, or a screw-typefeeder having a sealing capacity as described in co-pending applicationSer. No. 08/713,431.

[0092] Liquid, for example fresh water, steam, liquids containingcooking chemicals is introduced to vessel 81 via one or more conduits 82to produce a slurry of liquid and chips and to provide a detectableliquid level in vessel 81. Means for monitoring and controlling thelevel of the liquid, and the level of the chips, in vessel 81 may beprovided. This liquid may be a heated liquid, for example, hot water orsteam, having a temperature of between 50 and 100° C. If the vessel is apressurized vessel, liquid temperatures of over 100° C. may be used.Preferably, though not essentially, this liquid may contain at leastsome active pulping chemical, for example, sodium hydroxide (NaOH),sodium sulfide (Na2S), polysulfide, anthraquinone or their equivalentsor derivatives or surfactants, enzymes or chelants, or combinationsthereof.

[0093] From vessel 81, the slurry is discharged to the inlet of slurrypump 85 via conduit 84. The discharge from vessel 81 may be aided by adischarge device 83 (probably not necessary if a DIAMONDBACK® dischargeis used). The flow of slurry in conduit 84 may also be aided by theaddition of liquid via conduit 82′. The conduit 82′ may be the onlymechanism for introducing liquid, so that a liquid level is present inconduit 84 or not in vessel 81. Pump 85 may be any type of slurry pumpdiscussed above, for example, a Wemco or Lawrence pump or theirequivalents, any other type of solids or slurry transfer device. Thoughonly one pump 85 is shown, more than one pump or similar devices may beused to transfer the slurry via conduit 86 to vessel 321. The slurrytransfer via conduit 86 may include one or more storage or surge tanks(not shown). Preferably, the one or more pumps 85 include at least onedevice having de-gassing capability so that undesirable air or othergases may be removed from the slurry.

[0094] The slurry discharged from pump 85 is transferred via conduit 86to subsystem 810. Subsystem 810 may be located adjacent subsystem 710,that is, within about 30 feet of subsystem 710, or may be spaced anappreciable distance from subsystem 710, for example one-half mile ormore away, depending upon the layout of the pulp mill. Hence, conduit 86is broken to indicate an undetermined distance between subsystem 710 andsubsystem 810.

[0095] The pressure in conduit 86 is dependent upon the number of pumpsand other transfer devices used and the height and distance that theslurry must be transferred. The pressure in conduit 86 may vary fromabout 5 psig to over 500 psig.

[0096] Also, during transfer, the chips may be exposed to some form oftreatment, for example, de-aeration or impregnation with a liquid,preferably a liquid containing pulping chemicals, such as thosedescribed above. The slurry may also be exposed to at least one pressurefluctuation during transfer, such that the pressure of the slurry isvaried from a first pressure to a second, higher pressure, and then to athird pressure which is lower than the second pressure. As described inU.S. Pat. No. 4,057,461 and 4,743,338 varying the pressure of a slurryof chips and liquor improves the impregnation of the chips with theliquor. This pressure pulsation may be achieved via varying the outletpressure of a set of transfer devices in series, or by controlleddepressurization of the slurry between pumping.

[0097] The slurry in conduit 86 is introduced to the inlet of vessel321. Though the vessel shown is a treatment, i.e., steaming, vessel, itmay also be a storage vessel, an impregnation vessel, or even adigester. Since the transfer in conduit 86 typically requires that atleast some excess liquid, that is not needed during treatment orstorage, some form of de-watering device 87 may be located between thetransfer device and the treatment vessel. One preferred dewateringdevice is a Top Separator, as sold by Ahlstrom Machinery. This TopSeparator may be a standard type or an “inverted” Top Separator. Thisdevice may be an external stand-alone-type unit or one that is mounteddirectly onto the treatment vessel, as shown. Preferably, the liquidremoved from the slurry by means of de-watering device 87 is returned tovessel 82 or to the inlet of the pump, or pumps, 85 via conduit 88 toaid in slurrying the chips. This liquid removed via device 87 may alsobe used where ever needed in the pulp mill. This liquid in conduit 88may be heated or cooled as desired in a heat exchanger 90 and may bepressurized using one or more conventional centrifugal liquid pumps, 89.The liquid in conduit 88 may be introduced to vessel 81 via conduit 82and to conduit 84 via conduit 82′.

[0098] The treatment vessel 321 shown is a steaming vessel similar tovessel 221 shown in FIG. 3, for example a DIAMONDBACK® steaming vessel.The feed system 310 is otherwise similar to the system 210 shown in FIG.3. For example, chip feeding system 410, feeds digester feed system 310,which feeds digester 11. Note that system 310 of FIG. 4 is simply onesubsystem in the over-all system which feeds chips from the chip pile 80to the digester 11. This system may include one or more subsystems 310for feeding to digester 11.

[0099]FIG. 5 illustrates a further embodiment 610 that is an extensionof the system 510 shown in FIG. 4. The system 610 is a combination ofthree subsystems 710, 810 and 910. Subsystem 710 is similar to thesystem 410 of FIG. 4. Items in FIG. 5 that are essentially identical tothose found in FIGS. 1 through 4 are identified by the same numbers.

[0100] Wood chips 20, or some other comminuted cellulosic fibrousmaterial, from chip pile 80 are introduced with or without pressureisolation to vessel 81. The chips in vessel 81 may be treated with agas, such as steam or hydrogen sulfide, or a liquid, such as water or aliquid containing cooking chemical, introduced by way of one or moreconduits 82. Vessel 81 may be any type of vessel, but is preferably aDIAMONDBACK® bin, as described above. The treated chips are dischargedfrom vessel 81 into conduit 84. Though any type of discharging mechanismcan be used, the discharge of chips from vessel 81 is preferablyperformed without the aid of mechanical agitation or vibration, as ischaracteristic of DIAMONDBACK® chips bins. Conduit 84 may be any type ofpipe or chute but is preferably a curved Chip Tube as described above.

[0101] Conduit 84 introduces the chips to the inlet of slurry pump 85,which may be of the type supplied by Wemco or Lawrence, as describedabove. Typically, slurrying liquid is preferably first introduced to thechips in conduit 84, for example, using the conduit 82′, to produce alevel of liquid in vessel 81 or conduit 84. The liquid introduced viaconduit 82′, may be water or a liquid containing treatment chemicalssuch as kraft liquors, with or without strength or yield enhancingadditives. Make-up liquor, for example, liquor containing thesechemicals, is typically added via conduit 782.

[0102] The slurry in conduit 86 is introduced to subsystem 810 vialiquor separating device 887, which is similar in operation to device 87shown in FIG. 4. The liquid removed via separator 887 can be returned tosubsystem 710 via conduit 88 or can be used elsewhere in the pulp millvia conduit 888. If returned to subsystem 710 via conduit 88 the liquormay be augmented with additional liquid or chemical via conduit 788,heated via indirect heat exchanger 90 via conduit 790 and pressurized bypump 89 prior to being re-introduced to vessel 81 via conduit 82 or toconduit 84 via conduit 82′. Subsystem 710 may also include a liquorstorage tank similar to tank 353 shown in FIG. 4. Thus by the use ofheater 90 and chemical addition 782 or 788, the slurry of materialtransferred from subsystem 710 to subsystem 810 via conduit 86 may beheated to any desirable temperature while being treated with chemicals.For example, if the slurry in conduit 86 is heated to about 90° C. orabove in the presence of alkali or sulfide, some pretreatment of thewill occur during the retention time in conduit 86 prior to introductionof the slurry into subsystem 810. Of course, lower temperatures andother chemicals may also be used in conduit 86.

[0103] The chips retained by separator 887 are passed to vessel 821.Vessel 821 may be a vessel similar to vessel 81, but is preferably atall cylindrical vessel, for example, 20 to 50 feet tall, in which aliquid level 823 is maintained. A gas space 824 may be maintained abovelevel 823. Vessel 821 may be maintained at atmospheric pressure or atsuper-atmospheric pressure, for example, at 0.2 to 10 bar gauge pressure(e.g. about 5 bar), depending on the treatment performed in vessel 821.The temperature in vessel 821 may vary from 50 to 300° C., but istypically between about 50 and 150° C. Liquid may be introduced tovessel 821 via one or more conduits 822 or 860. This liquid may containcooking chemicals or additives as discussed above. These cookingchemicals or additives may be the same as those introduced in subsystem710 or they may be different. For example, kraft cooking liquorcontaining a high concentration of sulfide ion or sulfidity may beintroduced to subsystem 710 and kraft cooking chemical containing alower concentration of sulfide ion or sulfidity may be introduce to thechips in subsystem 810. In another example, a polysulfide-type additivemay be introduced to the chips in subsystem 710 and ananthraquinone-type additive may be introduced in subsystem 810.

[0104] The pressure within the vessel 821 may be monitored andcontrolled via pressure indicator and controller 825. Excess pressuremay be released via conduit 826, for example, to a conventionalnon-condensable gas (NCG) treatment system or to vessel 81 forpretreatment. In addition, the pressure controller 825 can be used toregulate the pressure in vessel 821 to vary the pressure to effectpressure pulsation impregnation as described in U.S. Pat. No. 4,057,461and 4,743,338.

[0105] The slurry is discharged from vessel 821 to conduit 850. Thisdischarge may be effected without agitation or vibration as in aDIAMONDBACK® chip bin, or it may be effected by agitation or vibrationas is conventional. Conduit 850 introduces the slurry to the inlet ofpump 851, which may be similar to pump 85, but typically will have ahigher pressure rating. Additional liquid may be introduced to conduit850 via conduit 854 to aid in introducing the slurry to the pump 851.The slurry discharged from pump 851 is passed to subsystem 910 viaconduit 886.

[0106] The slurry in conduit 886 is introduced to subsystem 910 usingthe liquor separating device 987. The separator 987 is similar todevices 887 and 87 (of FIG. 4). The liquor removed from device 987 maybe returned by conduit 911 to subsystem 810 or may be used elsewhere inthe pulp mill via conduit 988. If returned to subsystem 810 via conduit911, the liquor may be augmented with additional liquid or chemical viaconduit 912, heated via indirect heat exchanger 890 via conduit 891 andpressurized by pump 889 prior to being re-introduced to vessel 821 viaconduit 822 or 860 to conduit 850 via conduit 854. The liquor in conduit911 may also be introduced to subsystem 710, for example, via a commonconnection with conduit 88 or 82. Subsystem 810 may also include aliquor storage tank similar to tank 353 shown in FIG. 4. Thus by usingheater 890 and chemical addition 912, the slurry of material transferredfrom subsystem 810 to subsystem 910 via conduit 886 may be heated to anydesirable temperature while being treated with chemicals. For example,if the slurry in conduit 886 is heated to about 90° C. or above in thepresence of alkali or sulfide, some pretreatment of the material willoccur during the retention time in conduit 886 prior to introduction ofthe slurry into subsystem 910. Of course, lower temperatures and otherchemicals may also be used in conduit 886.

[0107] The chips retained by separator 987 are passed to vessel 921,which may be a vessel similar to vessels 81, or a tall vessel similar tovessel 821, or a vessel similar to vessel 321 of FIG. 4. Vessel 921 maybe maintained at atmospheric pressure, or at super-atmospheric pressure[for example, at 0.2 to 10 bar gauge, preferably 0.5 to 5 bar gaugepressure] depending on the treatment performed in vessel 921. Thetemperature in vessel 921 may vary from 50 to 300° C., but is typicallybetween about 50 and 150° C., preferably between about 80 and 120° C.Liquid may be introduced to vessel 921 via one or more conduits 922 or960. The introduced liquid may contain cooking chemicals or additives asdiscussed above. These cooking chemicals or additives may be the same asthose introduced in subsystem 710 or 810 or they may be different. Forexample, kraft cooking liquor containing a high concentration of sulfideion or sulfidity may be introduced to subsystem 810 and kraft cookingchemical containing a lower concentration of sulfide ion or sulfiditymay be introduced to the chips in subsystem 910. In another example, apolysulfide-type additive may be introduced to the chips in subsystem710 and an anthraquinone-type additive may be introduced in subsystem810, and kraft white liquor may be introduced to the chips in subsystem910. Each or these liquors can be isolated from each other by the liquorseparators 887 and 987.

[0108] The slurry is discharged from vessel 921 to conduit 950. Thisdischarge may be effected without agitation or vibration using adischarge as in a DIAMONDBACK® chips bin, or it may be aided byagitation or vibration as is conventional. Conduit 950 introduces theslurry to the inlet of pump 951, which may be similar to pumps 85 and851, but typically will have a higher pressure rating. Additional liquidmay be introduced to conduit 950 via conduit 960 to aid in introducingthe slurry to the pump 951. The slurry discharged from pump 951 ispassed to further treatment via conduit 986, for example, to a digester( that is, a continuous or batch digester), or to further treatment in asubsystem similar to subsystems 810 or 910, or subsystem 310 of FIG. 4.However, the treatment effected in subsystems 710, 810 and 910 may besufficient to produce an essentially fully-cooked pulp slurry in conduit950 such that no further “pulping” need be performed. The pulp inconduit 950 may be passed directly to washing and/or bleaching.

[0109] As in subsystems 310, 810, and 910, excess liquor may be returnedto subsystem 910 via conduit 913. The liquor may be augmented withadditional liquid or chemical via conduit 914, heated via indirect heatexchanger 990 via conduit 991 and pressurized by pump 989 prior to beingre-introduced to vessel 921 via conduit 922 or to conduit 950 viaconduit 960. The liquor in conduit 913 may also be introduced tosubsystem 710 or 810, for example, via a common connection with conduit88 or 82 (not shown) or a common connection with conduits 911 or 822, orsimilar conduits. Subsystem 910 may also include a liquor storage tanksimilar to tank 353 shown in FIG. 4.

[0110] Thus, using heater 990 and chemical addition 914, the slurry ofmaterial transferred from subsystem 910 to the subsequent subsystem ordigester via conduit 986 may be heated to any desirable temperaturewhile being treated with chemicals. For example, if the slurry inconduit 986 is heated to about 90° C. or above in the presence of alkalior sulfide, some pretreatment of the chips will occur during theretention time in conduit 986 prior to introduction of the slurry intothe subsequent treatment device, for example to digester 11 of FIGS. 1and 2. Of course, lower or higher temperatures and other chemicals mayalso be used in conduit 986.

[0111] Also, though indirect heat exchangers 90, 890, and 990 may eachbe supplied by their own separate source of heat, for example, separatesources of steam or hot water or hot effluent that would normally bedischarged, heat exchangers 90, 890 and 990 may also be supplied with acommon source of heat 915. The source of heat 915 may be, for example,hot effluent or steam (low, medium or high pressure steam), and may beintroduced to heat exchanger 990 and the residual heat transferred toheat exchanger 890 via conduit 992. The residual heat from heatexchanger 890 may be passed to heat exchanger 90 via conduit 892. Anyresidual heat remaining in conduit 92 may be used as needed in systems710, 810 or 910 or elsewhere in the mill, or it may be discarded. Forexample, the liquid in conduit 92, and any residual heat it may contain,may be introduced to vessel 81 or 821 via conduits 82 or 822 to recoverand re-use as much of the available energy as possible.

[0112] Using a system 610 as shown in FIG. 5, a counter-current flow oftreatment liquids can be established between each subsystem. Forexample, the liquid from upstream treatment can be returned to subsystem910 via conduit 913; the liquid from subsystem 910 can be returned tosubsystem 810 via conduit 911; and the liquid from subsystem 810 can bereturned to subsystem 710 via conduit 88. In addition some or all ofthese liquors can be removed and used elsewhere via conduits 888 and988.

[0113] The chemical addition at 788, 912, and 914 is preferably sodiumhydroxide, sodium sulfide; polysulfide, anthraquinone or theirequivalents or derivatives; surfactants, enzymes, or chelants; orcombinations thereof. For example, different treatment chemicals couldbe added at each of 788, 912, and 914, so that different treatments takeplace in each of the sections 710, 810, and 910. For example,polysulfide may be added at 788, anthraquinone at 912, and chelants andenzymes at 914. The conduits at 788, 912, 914 need not be provided whereillustrated in FIG. 5, but may be provided at any convenient locationwhich facilitates impregnation, or other pretreatment, simultaneouslywith transport. For example, lines 788, 912, 914 may be added to thelines 790, 891, 991 before the heater exchangers 90, 890, 990,respectively.

[0114] In one preferred embodiment, the slurry is treated in the systemof FIG. 5 to remove undesirable metal-containing compounds or metal ionsfrom the cellulose material. For example, in this embodiment thechemical added to the slurry is an acid and/or chelating agent. The acidis preferably sulfuric acid, sulfur dioxide, acetic acid, formic acid,oxalic acid, peroxy acids, Caro's acid, or their equivalents, orcombinations thereof. Acidic bleach plant filtrates can also be used asthe source of acid. The pH of the liquid during acid treatment typicallyvaries from a pH of about 1 to a pH of about 7, but is preferablybetween a pH of about 2 and about 4. The temperature of the acidtreatment may vary from about 0 to about 150° C., but is preferablybetween about 60 and about 90° C. The duration of the acid treatment maybe 10 minutes to 6 hours, but is preferably about 30 to 120 minutes. Theacid treatment may be followed by the addition of magnesium salts, forexample, magnesium sulfate, to replenish the magnesium content of thematerial which under certain conditions has been found to be beneficial.

[0115] The chelating agent, that is, a solution containing polydendateligand molecules, is preferably EDTA, DTPA, DTMPA, or their equivalents,or combinations thereof. The chelate charge is typically at most about 2kg per ton of pulp but may range from about 0.5 to 5 kg per ton of pulp.During chelate treatment, the pH of the treatment liquid typicallyvaries from a pH of about 2 to about 10, but is preferably between a pHof about 4 and about 8. The temperature of the chelate treatment mayvary from 0 to 150° C., but is preferably between about 60 and 110° C.The duration of the chelate treatment may be 10 minutes to 6 hours, butis preferably between about 30 to about 90 minutes.

[0116] The chelation stages (Q) and the acid stages (A) are not mutuallyexclusive; both types of treatments may be used, for example, insuccession (in either order) and repeatedly, during the transfer of theslurry of cellulosic material. Either treatment may also be practicedrepeatedly. The successive treatments may or may not include a purge orwashing stage between successive treatments. For example, some of thetreatment sequences that may be practiced according to this inventioninclude, but are not limited to, the following sequences: AA, QQ, AQA,QAQ, AAQ, QQA, AQQ, QAA, AAA, QQQ, AAQQ, QQAA. Repetition or extensionof these treatment sequences, as would be readily understood by those inthe art, is also within the scope of this invention. Again, thesesequences may or may not include a washing or purge between successivetreatments.

[0117] In the embodiment shown in FIG. 5, the acid or chelating agentcan be introduced via conduit 782, 788, 912, and/or 914, but the acid orchelate is preferably introduced to subsystem 710 via conduit 782 or tosubsystem 810 via conduit 912. If the acid or chelant is added tosubsystem 810, the metal removal treatment can be followed immediatelyby alkaline treatment in subsystem 910 prior to alkaline digestion in,for example, a digester (not shown) fed by conduit 986, with or withoutthe use of a conventional high-pressure feeder.

[0118] For example, after treatment or transport in subsystem 710, acidor chelant can be introduced to subsystem 810 via conduit 912, 854, 860,or 882. The acidified/chelated slurry is pressurized by pump 851 andpassed to liquor separator 987 via conduit 886. The treatment liquor canbe removed via separator 987 and returned upstream of the inlet of pump851 or, preferably, removed from the system via conduit 988. Themetal-laden stream removed via conduit 988 can be passed to othertreatment in the pulp mill or to disposal or to any suitable form ofconventional metal recovery process. The liquid removed via conduit 988may be removed simply through a branch conduit from conduit 911 or via aliquor separator, such as an In-line Drainer (not shown). The liquid inconduit 988 may also be removed directly from separator 987. The volumeof liquid removed via conduit 988 can be replaced, or “made up”, byliquid introduced via conduits 912, 854, 860 and/or 822, for example,water, washer filtrate, black liquor, or bleach plant effluent, amongother available liquids. Make-up acid or chelate may also be introduced,with or without make-up liquid, via one or more of the conduits 912,854, 860, and/or 822.

[0119] In addition, according to this invention, the acid or chelant canalso be introduced via conduit 782 or conduit 788 so that the metalremoval treatment is practiced in the subsystem 710 and a secondtreatment is practiced in subsystem 810 prior to alkaline treatment insubsystem 910. The second treatment in subsystem 810 may be a secondacid or a second chelate treatment, or, if the treatment in subsystem710 is an acid treatment, the treatment in subsystem 810 may be achelate treatment, or vice versa.

[0120] Furthermore, since the pH of the acid or chelate treatment willtypically be distinctly different from the pH of the alkaline treatment(for example, the alkaline treatment is typically practiced at a pHgreater than 8, often greater than 10), in order to avoid excessiveconsumption of acid, chelate, and/or alkali, in one embodiment of theinvention, the acid or chelate treatment in a first stage is followed bya wash or neutralization treatment in a following second stage, prior tothe subsequent treatment, for example, prior to the introduction ofalkaline liquids in a third stage. In the system shown in FIG. 5, theacid or chelate treatment can be practiced in subsystem 710, a somewhatneutral wash or soaking of the material can be practiced in subsystem810 and an alkaline treatment can be practiced in subsystem 910.

[0121] For example, acid or chelant can be introduced via conduit 782and the acidified/chelated slurry is pressurized by pump 85 and passedto liquor separator 887 via conduit 86. The treatment liquor can beremoved via separator 887 and returned to the inlet of pump 85 or,preferably, removed from the system via conduit 888. The metal-ladenstream removed via conduit 888 can be passed to other treatment in thepulp mill or to disposal or to a suitable conventional metal recoveryprocess. The liquid removed via conduit 888 may be removed simplythrough a branch conduit from conduit 88 or via liquor separator, suchas a conventional In-line Drainer (not shown). The liquid in conduit 888may also be removed directly from separator 887. The volume of liquidremoved via conduit 888 can be replaced, or “made up”, by liquidintroduced via conduits 788 and/or 782, for example, water, washerfiltrate, black liquor, or bleach plant effluent, among other availableliquids. Make-up acid or chelate may also be introduced, with or withoutmake-up liquid, via conduits 788 or 788 or both.

[0122] After acid or chelate treatment in subsystem 710, subsystem 810can be used to wash or neutralize the slurry prior to introducing theslurry to alkaline treatment in subsystem 910. For example, essentiallyneutral to alkaline, preferably metal-free, liquid can be introduced tothe slurry via conduit 912 or conduits 854, 860, or 822, to wash orincrease the pH of the slurry during passage through vessel 821 andthrough conduits 850 and 886 prior to introducing the slurry toseparator 987. The neutralized or pH-adjusted liquid is removed from theslurry via separator 987 and the liquid can be returned to upstream ofpump 851 via conduit 911 or removed via conduit 988. Again, the liquidremoved via conduit 988 may be removed via a simple branch conduit, viaa liquor separator (e.g., a conventional In-line Drainer) or directlyfrom separator 987.

[0123] After metal removal in subsystem 710 and washing orneutralization in subsystem 810, the cellulose material can be treatedwith alkaline cooking chemical, for example, kraft white, green, orblack liquor (with or without additives as discussed above) in subsystem910 prior to digestion with minimal excess use of chemical due toconsumption of acids and/or chelants by alkali.

[0124]FIG. 6 schematically illustrates other desirable apparatus forpracticing a desirable method according to the invention. Utilizing thesystem of FIG. 6 a slurry of comminuted cellulosic fibrous material(typically at a consistency of about 5-20%) is transported within a pulpmill at any locations within a fiber line, such as from the wood yard toa digester, with intermittent booster pumps in series. Each pump isassociated with a station (treatment vessel) and a solids/liquidseparator is associated with each station (typically a conventionalsolid/liquid separator at the top of the station), to isolate liquorstreams or circulations. Impregnation, or other pretreatment, isperformed simultaneously during transit of the material, in thecirculation lines (that is from one pump to its associated station), andthe lines can be made very long (e.g. more than 100 yards, up to about ahalf a mile) to facilitate that pretreatment and impregnation.Preferably heat exchangers are utilized on the return lines, anddegassing may be provided at one, more than one, or all of the transferstations. Also, an eductor (ejector) can be used in place a flash tankand/or control valves through which liquor is removed and pressurereduced. Further, pressurized pulsation action may be associated withthe configuration of pumps and stations, the pumps pressurizing theslurry to at least 5 bar (typically at least about 10 bar). Also, a widevariety of treatment chemicals may be utilized preferably added upstreamof the pumps, including sodium hydroxide, sodium sulfide; polysulfide,anthraquinone or their equivalents or derivatives; surfactants, enzymes,or chelants; or combinations thereof.

[0125] The chip slurry 1000 is formed in any conventional manner(including by heat steam slurrying), and first, second and third boosterpumps 1001, 1002, and 1003 are connected in series. The pumps 1001-1003are associated with stations (vessels) 1004, 1005, 1006, respectively.Preferably each of the stations 1004-1006 has a liquid/solid separatorassociated therewith. In the embodiment illustrated in FIG. 6 separators1007, 1008, 1009 are shown mounted at the top of each of the stations(treatment vessels) 1004-1006, although the separator could be atanother location, including the bottom.

[0126] Preferably chemical is added to the slurry at a number ofdifferent locations in the system, such as upstream at each of the pumps1001-1003. This is schematically illustrated by chemical addition atpoints 1010, 1011, and 1012 in FIG. 6. The same, or different, chemicalscan be added at each of 1010-1012. Preferably at least some of thechemical includes sodium hydroxide, sodium sulfide; polysulfide,anthraquinone or their equivalents or derivatives; surfactants, enzymes,or chelants; or combinations thereof. In the embodiment actuallyillustrated in FIG. 6, the chemical addition 1012 includes AQ ladenwhite liquor (e.g. vessel 1006 is a continuous digester).

[0127] Instead of establishing circulation lines such as illustrated inFIG. 5, circulation is provided in the FIG. 6 embodiment, in thepreferred form, so as to cause pseudo counter-current flow of thecomminuted cellulosic fibrous material and liquid. While FIG. 6illustrates three stations, any number of stations may be provided. Inthe embodiment in FIG. 6, the liquid removed from the separator 1007 inline 1013, is used elsewhere in the mill, or treated for reuse. Theliquid removed from separator 1008 passes in line 1014 to a pointupstream of the pump 1001 (e.g. it is diverted by the valve 1015 eitherto the slurrying station 1000, or to the infeed to the pump 1001) whileliquid separated by the third separator 1009 is circulated in line 1016to upstream of the pump 1002, e.g. diverted by the valve 1017 to thefirst station 1004, and/or to just upstream of the pump 1002. Freshliquor, from source 1012, is added to the bottom of the vessel 1005, orthe intake of the pump 1003.

[0128] In the return lines 1014, 1016, conventional indirect heatexchangers 1018, 1019 may be provided which change the temperature ofthe liquid therein by at least 5° C. In the embodiment illustrated, theliquor is heated, but in some circumstances the liquid could be cooledinstead of heated. A indirect heat exchanger 1020 may be also beassociated with the chemical addition 1012.

[0129] Liquor can be passed from the third station 1006 (which may be adigester-e.g. black liquor) through a conventional eductor (ejector)1022, rather than a flash tank and/or control valves. Each of the pumps1001-1003 preferably pressurizes the slurry to a pressure of at least 5bar (typically at least about 10 bar).

[0130] Degassing may also be associated with one, more than one, or allof the stations 1004. This is schematically illustrated by the gasremoval lines 1023-1025 in FIG. 6. Degassing may be accomplished usingany conventional degassing equipment, associated with the separator1007-1009, the inlet line, or the like.

[0131]FIG. 7 schematically illustrates a continuous digester feed systemsimilar to the system illustrated in FIG. 3. Some of the significantdifferences between the system of FIG. 7, and the method practicedthereby, and the system of FIG. 3, and the method practiced thereby, arethe provision of a cooling heat exchanger and a return line from thedigester to one or more pumps, a return conduit for introducing liquordirectly into the chip tube (by bypassing the surge tank), and arecirculation conduit from the outlet of one or each slurry pump(including the first pump) ultimately to the inlet thereof (e.g.connected between the surge tank and the chip tube for the first pump)to establish a recirculation flow that is particularly desirable duringthe startup operation.

[0132] It is to be understood that though a continuous digester isillustrated in FIG. 7, the present invention is also applicable to abatch digester system. The system shown in FIG. 7 includes a feed system1110 feeding a digester 1111. The feed system 1110 includes an air-lockchip feed screw 1112, for accepting wood chips 20, and chip bin 1121.Feed screw 1112 is preferably the device disclosed in U.S. Pat. No.5,766,418 and bin 1121 is marketed under the name Diamondback® SteamingVessel or Bin as discussed above. Other types of conventional steamingvessels, for example, horizontal screw conveyors or VibraBin vesselshaving a vibrating discharge, may also be used in place of a DiamondbackBin.

[0133] Similar to the system shown in FIG. 3, the system shown in FIG. 7includes a metering device 1123, such as a Chip Meter, a verticalconduit 1126, such as a Chip Tube, and a liquor storage vessel 1153,such as Liquor Surge Tank. Also, as shown in FIG. 3, the system of FIG.7 includes a first pump, or pumping device, 1151 and a second pump, orpumping device, 1151′, which again, may be any type of pump or pumpingdevice for pressurizing and transferring a slurry of comminutedcellulosic fibrous material and liquid. One preferred pumping device isa Hidrostal screw-feed-type pump provided by Wemco Pump of Salt LakeCity, Utah, [http://www.wemcopump.com/Products/hidrostal/details. html]or a pump provided by Lawrence Pumps Inc. of Lawrence, Mass.[http://www.lawrencepumps.com/]. Similar to the system shown in FIG. 3,the inlet of pump 1151 is in operative communication or is connecteddirectly to the outlet of vertical conduit 1126 and the outlet of pump1151 is in operative communication with or is connected to the inlet ofpump 1151′. The outlet of pump 1151′ is operative communication with theinlet of digester 1111 via conduit 1134. Excess liquor is returned fromthe digester 1111 to the feed system 1110 from the inlet of thedigester, or from any other available source of liquid associated withthe digester, via conduit 1135.

[0134] Though not shown in FIG. 7, it would be recognized by thosefamiliar with the art, that the present invention may also be practicedby having the one or more pumps 1151 feed two or more pumps 1151′ forfeeding one or more digesters 1111. This mode of operation may beparticularly suitable for feeding a plurality of batch digesters, butmay also be applicable to feeding two or more continuous digesters. Onedevice that can be used to split the flow from one conduit to two ormore conduits is shown in FIG. 8. It is also recognized that the presentinvention may also incorporate the features of the inventions disclosedin U.S. Pat. No. 5,795,438, the disclosure of which is incorporated inits entirety by reference herein.

[0135] Liquor in conduit 1135 is returned to various locations in thefeed system 1110. The liquor in conduit 1135 is preferably returned toChip Tube 1126 via conduit 1182 or to tank 1153 via conduit 1183 or tovessel 1121 via conduit 1184. Since the liquor in conduit 1135 willtypically have a temperature greater than 100° C. and the Chip Tube 1126and vessel 1153 may operate at approximately atmospheric pressure, thatis, −1 to 1 bar gage (that is, 0 to 2 bar absolute), to avoidundesirable rapid evaporation (that is, “flashing”), some form ofcooling device 1136 is provided. This cooling device is preferably anindirect liquor-to-liquor cooling heat exchanger, and cools the liquidbeing returned to below the temperature at which it will flash. Thecooling medium provided in conduit 1137 is typically any available coolliquid stream in the pulp mill. One preferred cooling medium is freshwater which is introduced via conduit 1137 to heat exchanger 1136 at onetemperature and removed via conduit 1138 at a higher temperature.Cooking liquids, for example, kraft white, green, or black liquor (forexample, via conduit 1150) may also be used as the cooling medium inheat exchanger 1136. A bypass conduit 1135′ may also be used to divertliquor around heat exchanger 1136 when the heat exchanger is not neededor when it is being serviced.

[0136] The level of liquid in tank 1153 is typically controlled by alevel control mechanism, for example, a level control mechanism using ad-p cell level indicator or a gamma radiation level indicator (notshown). The level in tank 1153 is typically controlled by varying theflow of liquid out of branch conduit 1181 which feeds pump 1160, thatis, the Make-up Liquor pump. Pump 1160 pressurizes and introduces thisexcess liquor to the top of the digester 1111 via conduit 1161.

[0137] Liquor in conduit 1135 may also be introduced, with or withheating or cooling, upstream of pump 1151 via conduit 1163. Conduit 1163may have a valve F. The benefit of introducing pressurized liquid fromconduit 1135 upstream of pump 1151 is discussed above in the descriptionof FIG. 3. The present invention also preferably includes a conduit 1156between the outlet of pump 1151 and conduit 1154 which may have a valveE, so that liquor may flow from line 1156 to line 1154.

[0138] Liquor may also be introduced to conduits 1134 and 1135 viaconduits 1144 and 1145 during normal operation or during shutdown orstartup of the system. For example, weak black liquor or “cold blow”liquor from pump 1140 may be introduced to conduits 1134 and 1135 toflush the lines during shutdown or to introduce additional liquor to thelines as needed, for example, for liquor-to-wood ratio control or blackliquor pretreatment, during normal operation. Cooking liquor, forexample, kraft white liquor, green liquor, black liquor, orange liquor,or liquor containing strength or yield enhancing additives, such asanthraquinone, polysulfide, chelants, surfactants, sulfur, or theirderivatives and equivalents, may be added to feed system 1110 viaconduit 1150 and pump 1152. The liquor in conduit 1150 is preferablyadded to Chip Tube 1126 as shown, but can also be added to conduits 1134or 1135.

[0139] The system shown in FIG. 7 also includes several valves, eitherautomatically controlled or manual, which isolate the flow of liquidsand their pressures from each other. Valve A isolates the outlet of pump1151 from the inlet of pump 1151′. Valve B isolates the outlet of pump1151′ from the digester 1111. Valve C in conduit 1134 isolates the feedconduit to the digester 1111 from the digester and valve D in conduit1135 isolates the return conduit 1135 from the digester 1111. Thesevalves are especially important during upset conditions to isolate thehot pressurized liquids associated with the digester 1111 from the lowerpressure feed system 1110 and from the surrounding personnel andadjacent machinery.

[0140] The valves A-F, along with selected other valves, can also beused to isolate liquor circulations to aid in start-up and shutdownprocedures. For example, when valve A is closed and valve E in conduit1156 is open, pump 1151 can be started and a closed circulation aboutpump 1151 can be established via conduit 1156. Similarly, when valve Ais closed and valves C, D, and F are opened and pump 1151′ is started, acirculation about pump 1151′ can be provided via conduit 1134, the topof digester 111, conduit 1135, and conduit 1163. (It is also possible toisolate the circulation about pump 1151 from the digester 1111 byinserting a conduit 1170, with an appropriate valve G, in conduit 1170between conduits 1134 and 1135.)

[0141] The conduits 1156, 1154 (and preferably the isolating Valves Aand E), and associated connections to other components, comprise meansfor circulating liquid from the pump 1151 outlet back to its inlet.While conduits are shown as such means it is to be understood that anyconventional structures which provide this recirculation may beutilized, including tanks, ejectors, pumps, valves, ducts, heatexchangers, or the like.

[0142] Isolation of these circulations is especially advantageous duringstart-up and shutdown conditions when these isolations can be separatelymaintained. For example, during start-up, before the introduction ofwood chips, the two pumps 1151, 1151′ can be operated to establish onecirculation about pump 1151 via conduit 1156 and a second circulationabout pump 1151′ passing through the digester top and conduits 1134 and1135. By so doing, the proper operation of each pump 1151, 1151′ can beverified and also the pressures and temperatures of each circulation canbe isolated For example, the temperature and pressure of the liquid inthe circulation in conduits 1134 and 1135 can be raised to digesteroperating conduits, for example, 7-15 bar gage at 100-160° C., while thetemperature of the circulation associated with pump 1151 and conduit1156 can be maintained at lower conditions, for example, 1-3 bar gage at60-120° C. Then when the conditions in each circulation agree, forexample, the liquor in conduits 1134 and 1156 are both at about 10 bargage and 120° C., valve A can be gradually opened while valve E isgradually closed and chips can be introduced to feed system 1110. Asimilar situation can occur during shutdown or when the digester 1111and/or feed system 1110 need to be isolated for servicing.

[0143] Feed system 1110 may also include a centrifugal separator forremoving sand and debris, for example, a Sand Separator; a liquor/chipsseparator, for example, an In-line drainer; or a liquor storage vessel,for example, a Level Tank, if needed, as found in conventional systems.One or all of these devices may also be omitted from the embodimentshown in FIG. 7.

[0144] Feed system 1110 may also include an integral Chip Tube and SurgeTank, as well as other simplifications to a feed system, as disclosed inco-pending application Ser. No. 09/520,761 filed on Mar. 7, 2000(attorney ref. 10-1302), the disclosure of which is incorporated byreference in its entirely herein.

[0145] FIGS. 8-10 illustrate another embodiment of the present inventionfor dividing the flow of slurry in a pipe line. FIG. 8 illustrates anelevation view, FIG. 9 a top view, and FIG. 10 a right-hand elevationview. The device 1200 shown in FIGS. 8-10, which is referred to as astatic “flow divider” or “flow splitter”, can, for example, be insertedin conduit 34 of FIGS. 1 and 2, conduit 252 or 234 of FIG. 3, conduit 86and 886 of FIGS. 4 and 5, or corresponding conduits in FIG. 6, orconduit 1134 in FIG. 7.

[0146] The static flow splitter 1200 includes an inlet 1201 for a flowof a slurry of comminuted cellulosic fibrous material and liquid and twoor more outlets 1202, 1203. The inlet and outlets are preferablycircular in cross section, but may be non-circular depending upon theneeds of the installation, including elliptical, rectangular, square, oreven triangular. The device 1200 includes a chamber 1204 for receivingthe slurry from the inlet 1201 and discharging the slurry to the two ormore outlets 1203, 1204. The chamber 1204 can have any appropriate crosssectional shape, including round, elliptical, rectangular, square, ortriangular, but the shape of the chamber preferably limits the areas inwhich material in the slurry can stagnate, for example, sharp cornersare avoided. As shown in FIG. 8, one preferred shape of chamber 1204 issubstantially triangular in which the outlets 1202, 1203 havecenterlines that diverge from the centerline of the inlet 1201 bybetween about 30 and 60°, for example, by about 45°.

[0147] The chamber 1204 may also include one or more internal baffleplates 1210, 1211 (shown in phantom) in FIG. 8 to aid in directing theflow of slurry to the two or more outlets 1202, 1203. These baffleplates 1210, 1211 may define a triangle with the wall 1212, positionedopposite the inlet 1201 of device 1200. The ends of the plates 1210,1211 may be welded or otherwise attached to the walls 1213, 1214 of thechamber 1204. In the embodiment illustrated in FIG. 8 the apex 1215 ofthe substantially triangular baffle plate arrangement 1210, 1211 issubstantially aligned with the inlet 1201. The flow splitter 1200 isstatic, i.e. has no moving parts (although the position of the baffleplate arrangement 1210, 1211 may be made adjustable).

[0148] The dimensions of device 1200 will vary depending upon the givenor desired dimensions and production rate of the system in which it isused. The dimension, for example diameter, of the inlet 1201, and theoutlets 1202, 1203, may range from 2 inches to 10 feet. For example, theinside diameter of the inlet and outlets is about 10 inches. Thedimensions of the chamber 1204 will be essentially dictated by thedimensions of the inlet and outlet, an may also vary from about 2 inchesto about 10 feet, for example, the chamber 1204 shown in FIGS. 8-10 hasa width of about 13 inches.

[0149] Device 1200 is typically made of any appropriate material thatcan withstand the hot (for example, 400° F. or hotter), pressurized (forexample, 300 psig or greater), corrosive (either acidic or alkaline)slurries that are typically handled in a pulp and paper mill, includingmetals and high-performance plastics. However, the device is preferablymade of metal, in particular steel, and is preferably made from weldablestainless steel, for example 304L (having an ASTM designationASTM-A240-304L), or its equivalents, or better.

[0150] In use, the inlet 1201 is connected to the conduit 34, 252, 234,86, 856, 1134, and one outlet 1202 is connected to the same conduitwhile the other outlet 1203 is connected to a conduit leading to thesame or another digester (batch or continuous). Where only two outlets1202, 1203 are provided preferably about one-half the inlet flow goes toeach, although the plates 1202, 1203 may be dimensioned or positioned,so that a higher volume flow goes through one outlet 1202, 1203 than theother.

[0151] In the broadest aspect of this invention, a system and method areprovided for the multistage transport and treatment of comminutedcellulosic fibrous material with the economical recovery and re-use ofenergy, including thermal energy.

[0152] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A system for producing chemical cellulose pulpfrom comminuted fibrous cellulose material, comprising: a steamingvessel in which comminuted fibrous cellulose material is steamed toremove the air therefrom; a superatmospheric pressure vertical treatmentvessel having an inlet for a slurry of comminuted cellulose fibrousmaterial at a top portion thereof and an outlet at a bottom portionthereof; pressurizing transfer means for pressurizing a slurry ofmaterial from the steaming vessel and transferring it to said treatmentvessel inlet, said pressurizing transfer means consisting of one or morehigh pressure slurry pumps, each having an inlet and outlet, locatedbelow said top portion of said treatment vessel; and means forcirculating liquid from the outlet of at least one said high pressureslurry pump to the inlet thereof.
 2. A system as recited in claim 1further comprising a liquid return line from said top portion of saidtreatment vessel, said return line operatively connected to an inlet oroutlet of one of said slurry pumps.
 3. A system as recited in claim 2further comprising a heat exchanger located in said return line.
 4. Asystem as recited in claim 3 wherein said heat exchanger is a heatexchanger for cooling or heating the liquid in the return line.
 5. Asystem as recited in claim 3 wherein said heat exchanger is aliquid-liquid indirect heat exchanger; and further comprising a sourceof cool liquid connected to said heat exchanger, for cooling the liquidin said return line.
 6. A system as recited in claim 1 furthercomprising a slurrying vessel having an inlet operatively connected tosaid steaming vessel and an outlet operatively connected to the inlet ofsaid one or more slurry pumps.
 7. A system as recited in claim 6 furthercomprising a liquid return line from said top portion of said treatmentvessel, said return line operatively connected to said slurry vessel. 8.A system as recited in claim 7 further comprising a heat exchangerlocated in said return line.
 9. A system as recited in claim 8 whereinsaid heat exchanger is an indirect heat exchanger for cooling or heatingthe liquid in the return line.
 10. A system as recited in claim 1wherein said at least one pump comprises at least two pumps.
 11. Asystem as recited in claim 10 wherein each of said pumps has a saidcirculation means.
 12. A system as recited in claim 1 wherein saidcirculation means comprises a conduit having a first valve therein, andfurther comprising a second valve between said pump outlet and saidtreatment vessel.
 13. A method as recited in claim 11 wherein each ofsaid circulation means comprises a conduit having a first valve therein,and further comprising a second valve between said pump outlet and saidtreatment vessel.
 14. A system as recited in claim 10 wherein saidtreatment vessel comprises a first vessel, and further comprising asecond treatment vessel; a main conduit connected to said outlet of saidat least one pump; a static flow splitter having an inlet and at leasttwo outlets; said main conduit connected to said flow splitter inlet;and one of said flow splitter outlets connected to said first treatmentvessel and another outlet to said second treatment vessel.
 15. A systemas recited in claim 14 wherein said flow splitter comprises a chamberhaving a substantially triangular shaped static baffle plate arrangementwith a triangle apex substantially aligned with said inlet.
 16. A methodof feeding comminuted cellulosic fibrous material to the top of atreatment vessel comprising the steps of: (a) steaming the comminutedcellulosic fibrous to remove air therefrom and to heat the material; (b)slurrying the comminuted cellulosic fibrous material with a cookingliquor to produce a slurry of liquid and material; and (c) pressurizingthe slurry at a location at least thirty feet below the top of thetreatment vessel and transferring pressurized material to the top of thetreatment vessel, said pressurizing step consisting of acting on theslurry with two or more high pressure slurry pumps.
 17. A method offeeding comminuted cellulosic fibrous material to the top of a treatmentvessel, comprising: (a) steaming the material to remove air therefromand to heat the material; (b) slurrying the material with a cookingliquor to produce a slurry of liquid and material; (c) pressurizing theslurry at a location at least thirty feet below the top of the treatmentvessel and transferring pressurized material to the top of the treatmentvessel, said pressurizing step consisting of acting on the slurry withone or more high pressure slurry pumps; and (d) establishing arecirculation loop between the pump outlet and inlet during startup. 18.A method as recited in claim 17 wherein a first valve is provided in therecirculation loop and a second valve between the pump outlet and thetreatment vessel; and wherein (d) is practiced to open the first valveand at least partially close the second valve during startup; andfurther comprising: (e) after startup closing the first valve andopening the second valve.
 19. A method as recited in claim 17 furthercomprising (e) returning liquid from the treatment vessel to the pumpinlet, and (f) positively cooling the returning liquid so that it has atemperature below the point at which it will flash during handling. 20.A method as recited in claim 17 further utilizing a second treatmentvessel; and further comprising (e) statically splitting the flow ofliquid from the outlet of the last of the pumps to direct part of theflow to each treatment vessel.
 21. A method as recited in claim 16 (d)establishing a recirculation loop between each pump outlet and inletduring startup.
 22. A method as recited in claim 21 wherein a firstvalve is provided in each recirculation loop and a second valve betweeneach pump outlet and each treatment vessel; and wherein (d) is practicedto open each first valve and at least partially close each second valveduring startup; and further comprising: (e) after startup closing eachfirst valve and opening each second valve.
 23. A method as recited inclaim 16 further comprising (e) returning liquid from the treatmentvessel to the pump inlet, and (f) positively cooling the returningliquid so that it has a temperature below the point at which it willflash during handling.